It has been customary in the past to make tire sidewalls using sidewall packages having a white polymeric blend composition. The polymeric blend composition is generally a blend of natural rubber, chlorobutyl, EPDM, and various other ingredients. A whitener having a high opacity, titanium dioxide, is generally added to mask the color of the blend composition. This further increases the brightness of the composition as well.
In the past, calcium sulfate has been added as a filler to such white polymeric blend compositions in addition to other additives, such as the whitener. Further, it has been known to use calcium sulfate as a white pigment in polystyrene resins used as paper coatings as is taught in U.S. Pat. No.3,873,521 to Tatsua et.al., or as a white pigment in a synthetic latex such as a diene derivative polymer used as a paper coating as taught in U.S. Pat. No. 4,425,452 to Nakata et.al. However, it has not been known that the titanium dioxide content could be reduced and replaced with a complementary amount of calcium sulfate.
Since the supply of titanium dioxide is sometimes less than the demand, it is an advantage to find a substitute for titanium dioxide as a whitener.